Motor driving circuit, motor device, and electric vehicle

ABSTRACT

A motor driving circuit has a supply line connected to a DC power source, an inverter whose input side is connected to the supply line and whose output side is connected to a motor, a power switch inserted in the supply line for switching the supply line between conducting and cut-off states, a voltage detector for detecting a voltage between the direct-current power source and the power switch, and an insulation resistance detector for first detecting, based on a result of detection by the voltage detector with the power switch in the cut-off state, an insulation resistance on the preceding-stage side of the power switch and subsequently detecting, based on a result of detection by the voltage detector with the power switch in the conducting state, an insulation resistance on the succeeding-stage side of the power switch.

TECHNICAL FIELD

The present invention relates to motor driving circuits, motor devices,and electric vehicle.

BACKGROUND ART

Conventionally, as a motor driving circuit for use on an electricvehicle or the like, one having a function of detecting insulationresistance has been proposed. With such a motor driving circuit, forexample, on detection of dielectric breakdown, appropriate measures canbe taken so that the resulting trouble may be avoided as much aspossible. Patent Document 1 identified below discloses an electricautomobile system in which, while a controller monitors the voltages ofa high-voltage battery and an auxiliary battery, a voltage converter andan electromechanical system are operated in coordination to achievenecessary control. Patent Document 2 identified below discloses a devicecomprising means for detecting an induced voltage ascribable to anelectric leak so that, on detection of an induced voltage, the supply ofpower may be shut off.

LIST OF CITATIONS Patent Literature

Patent Document 1: JP-A-2005-73443

Patent Document 2: JP-A-H9-117050

SUMMARY OF THE INVENTION Technical Problem

A motor driving circuit having a function of detecting insulationresistance can be configured, for example to enable it to identify thelocation of dielectric breakdown with certain exactitude, so as todetect insulation resistance separately for different portions.Inconveniently, however, providing a separate circuit for insulationresistance detection for each such portion complicates the configurationof the motor driving circuit, and may invite increased production costs.Incidentally, neither Patent Document 1 nor Patent Document 2 teaches aconfiguration that detects insulation resistance on a portion-by-portionbasis.

Against the background discussed above, an object of the presentinvention is to provide a motor driving circuit that detects insulationresistance on a portion-by-portion basis and that nevertheless allowseasy simplification of circuit configuration, and to provide a motordevice and an electric vehicle provided with such a motor drivingcircuit.

Means for Solving the Problem

According to one aspect of the present invention, a motor drivingcircuit is provided with: a supply line connected to a direct-currentpower source; an inverter of which the input side is connected to thesupply line and of which the output side is connected to a motor, theinverter converting direct-current electric power fed from the supplyline into alternating-current electric power and feeding thealternating-current electric power to the motor; a power switch insertedin the supply line for switching the supply line between a conductingstate and a cut-off state; a voltage detector for detecting the voltagebetween the direct-current power source and the power switch; and aninsulation resistance detector for first performing a first detectionoperation to detect, based on the result of detection by the voltagedetector with the power switch in the cut-off state, an insulationresistance on the preceding-stage side of the power switch, andsubsequently performing a second detection operation to detect, based onthe result of detection by the voltage detector with the power switch inthe conducting state, an insulation resistance on the succeeding-stageside of the power switch.

Advantageous Effects of the Invention

With a motor driving circuit according to the present invention, it ispossible to detect insulation resistance on a portion-by-portion basis,and in addition allows easy simplification of circuit configuration.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration diagram of a motor device according to a firstembodiment of the present invention;

FIG. 2 is a flow chart of insulation resistance detection operationaccording to the first embodiment;

FIG. 3 is a configuration diagram of a motor device according to asecond embodiment of the present invention; and

FIG. 4 is a flow chart of insulation resistance detection operationaccording to the second embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, motor devices embodying the present invention will bedescribed by way of a first and a second embodiment. The firstembodiment is for driving one motor, and the second embodiment is fordriving a plurality of motors (presented will be an example involvingtwo motors).

1. First Embodiment Configuration and Other Features of a Motor Device

First, a first embodiment of the present invention will be described.FIG. 1 is a configuration diagram of a motor device 9 according to thisembodiment. The motor device 9 is composed of a motor driving circuit 1and a motor 2 connected to it. The motor device 9 is provided on anelectric vehicle (such as an electric bicycle, a two-wheeled motorvehicle, a three-wheeled motor vehicle, or a four-wheeled motorvehicle), and the motor 2 serves to rotate a driving wheel of such anelectric vehicle.

The motor driving circuit 1 has a DC (direct-current) power source 1 a,a power supply circuit 1 b, and an inverter circuit 1 c. The powersupply circuit 1 b, the inverter circuit 1 c, and the motor 2 are housedin separate metal cases (5 a to 5 c) respectively. These metal cases (5a to 5 c) are connected together via the body frame of the electricvehicle. In the present description, unless otherwise stated, within themotor driving circuit, a “preceding-stage side” refers to a side closerto the DC power source, and a “succeeding-stage side” refers to a sidecloser to the motor.

The DC power source 1 a is, for example, a battery for an electricvehicle. The positive electrode side of the DC power source 1 a isconnected to a positive line L1 (supply line), and the negativeelectrode side of the DC power source 1 a is connected to a negativeline L2 (ground line). The voltage of the DC power source 1 a (thebattery voltage) is previously known. The DC power source 1 a, the powersupply circuit 1 b, and the inverter circuit 1 c are connected togethervia the positive line L1 and the negative line L2.

The power supply circuit 1 b has four resistors (11 to 14), a controller15, two normally-open switches (Sw1, Sw2), and a power switch Sw3.

The power switch Sw3 is a FET (field-effect transistor), the channelacross whose both terminals (source and drain) is controlled between anopen and a closed state (an on and an off state) by the controller 15.The power switch Sw3 is inserted in the positive line L1, and serves toswitch the positive line L1 between a conducting and a cut-off state.

The normally-open switches (Sw1, Sw2) are each a photoMOS relay, thechannel across whose both terminals (source and drain) is controlledbetween an open and a closed state (an on and an off state) by thecontroller 15. One end of the normally-open switch Sw1 is connected viathe resistor 11 to the positive line L1 (on the preceding-stage side ofthe power switch Sw3), and the other end of the normally-open switch Sw1is connected to one end of the resistor 12. The other end of theresistor 12 is connected to one end of the resistor 13. One end of thenormally-open switch Sw2 is connected to the other end of the resistor13, and the other end of the normally-open switch Sw2 is connected viathe resistor 14 to the negative line L2.

The connection point between the resistors 12 and 13 is connected to thebody frame of the electric vehicle. The connection point between thenormally-open switch Sw2 and the resistor 14 is connected to thecontroller 15. Thus, when the normally-open switches (Sw1, Sw2) are bothin the closed state, the controller 15 can detect a voltage value Vdwhich results from division of the voltage between the positive line L1and the negative line L2 by the resistors (11 to 14).

The portion of the power supply circuit 1 b constituted by the resistors(11 to 14) serves as an insulation resistance detection circuit, and theresult of the detection of the voltage value Vd is used in the detectionof insulation resistance (resistance with respect to the metal cases orthe body frame). Specifically, if there is any location with a lowinsulation resistance (a location of dielectric breakdown), the voltageof the DC power source 1 a is applied via the body frame or the metalcases to the insulation resistance detection circuit, and this producesa variation in the voltage value Vd, making it possible to detect theinsulation resistance. The operation for detecting insulation resistance(insulation resistance detection operation) will be described in detaillater.

The inverter circuit 1 c is provided on the succeeding-stage side of thepower supply circuit 1 b. The inverter circuit 1 c is supplied with a DCvoltage from the DC power source 1 a, and serves to convert the DCvoltage into a three-phase AC (alternating-current) voltage to output itto the motor 2. The inverter circuit 1 c has a smoothing capacitor 21and also three-phase arms comprising a U-phase, a V-phase, and a W-phasearm.

One end of the smoothing capacitor 21 is connected to the positive lineL1, and the other end of the smoothing capacitor 21 is connected to thenegative line L2. The U-phase, V-phase, and W-phase arms are connectedin parallel, each between the positive line L1 and the negative line L2.

The U-phase arm has two switching devices (Sw4 and Sw5) connected inseries between the positive line L1 and the negative line L2 and twodiodes connected in parallel with those switching devices (Sw4 and Sw5)respectively. Each diode is arranged with its cathode pointing to thepositive line L1 and its anode pointing to the negative line L2. Theswitching device Sw4 corresponds to an upper-arm switch (upper device)of the U phase, and the switching device Sw5 corresponds to a lower-armswitch (lower device) of the U phase.

The V-phase arm has two switching devices (Sw6 and Sw7) connected inseries between the positive line L1 and the negative line L2 and twodiodes connected in parallel with those switching devices (Sw6 and Sw7)respectively. Each diode is arranged with its cathode pointing to thepositive line L1 and its anode pointing to the negative line L2. Theswitching device Sw6 corresponds to an upper-arm switch (upper device)of the V phase, and the switching device Sw7 corresponds to a lower-armswitch (lower device) of the V phase.

The W-phase arm has two switching devices (Sw8 and Sw9) connected inseries between the positive line L1 and the negative line L2 and twodiodes connected in parallel with those switching devices (Sw8 and Sw9)respectively. Each diode is arranged with its cathode pointing to thepositive line L1 and its anode pointing to the negative line L2. Theswitching device Sw8 corresponds to an upper-arm switch (upper device)of the W phase, and the switching device Sw9 corresponds to a lower-armswitch (lower device) of the W phase.

The switching devices (Sw4 to Sw9) constituting the inverter circuit 1 care each a FET, the channel across whose both terminals (source anddrain) is controlled between an open and a closed state (an on and anoff state) by the controller 15.

The motor 2 is, for example, a three-phase permanent-magnet synchronousmotor, and is driven by the three-phase AC voltage fed from the invertercircuit 1 c. The motor 2 has three-phase lines 2 a, which comprise aU-phase, a V-phase, and a W-phase line, and these lines are connectedtogether inside the motor 2. The U-phase, V-phase, and W-phase lines areconnected to, inside the inverter circuit 1 c, between the upper andlower arms of the U, V, and W phases respectively.

The controller 15 provided in the power supply circuit 1 b can outputcontrol signals to control the switches (Sw1 to Sw9) individuallybetween the on and off states, and controls the operation of the motordriving circuit 1 through a prescribed procedure. One example of theoperation performed by the motor driving circuit 1 is insulationresistance detection operation for detecting whether or not theinsulation resistance of the motor device 9 is satisfactory or not.

[Insulation Resistance Detection Operation]

In an electric vehicle incorporating the motor device 9, when anignition key is turned on, the vehicle goes through a predeterminedstart-up mode into a running mode in which it can run. In the start-upmode, the motor driving circuit 1 performs insulation resistancedetection operation. Now, the insulation resistance detection operationperformed by the motor driving circuit 1 will be described withreference to a flow chart in FIG. 2. At the stage before the start ofthe insulation resistance detection operation, the switches (Sw1 to Sw9)are all off.

First, the controller 15 executes an insulation resistance sensorstart-up conformation (step S1). The insulation resistance sensorstart-up conformation is operation performed, before closing thenormally-open switches (Sw1, Sw2), to check whether or not the detectedvalue of the voltage Vd is normal (whether or not it falls within atolerated error range with respect to 0 V). If the detected value of thevoltage Vd is abnormal, for example, an alarm indicating the abnormalitycan be given off, and the insulation resistance detection operation canbe aborted.

Next, the controller 15 turns on both normally-open switches (Sw1, Sw2)(step S2). As a result, the positive line L1 is connected via theresistors 11 and 12 to the body frame, and the negative line L2 isconnected via the resistors 13 and 14 to the body frame. At this stage,the power switch Sw3 is still off, and accordingly the portion on thesucceeding-stage side of the power switch Sw3 (the inverter circuit 1 cand the motor 2) does not conduct to the positive electrode of the DCpower source 1 a.

In this state, the controller 15 checks whether or not the voltage valueVd falls within a prescribed normal range (step S3). This operation isaimed at checking whether or not the insulation resistance of the powersupply circuit 1 b (the portion on the preceding-stage side of the powerswitch Sw3) is satisfactory. The normal range is determined withconsideration given to, for example, fluctuations in the voltage of theDC power source 1 a so that it is possible to properly detect whether ornot the insulation resistance is satisfactory.

When the insulation resistance in the power supply circuit 1 b issufficiently high (normal), the voltage value Vd is close to the valueof the voltage resulting from division of the voltage of the DC powersource 1 a by the resistors (11 to 14). However, the lower theinsulation resistance (that is, the more serious the abnormality), thefarther the voltage value Vd deviates from the value of the voltageresulting from division of the voltage of the DC power source 1 a by theresistors (11 to 14).

Based on this principle, the controller 15 recognizes, when the voltagevalue Vd falls within the normal range (step S3, Y), that the insulationresistance of the power supply circuit 1 b is normal (no dielectricbreakdown has occurred) and, when the voltage value Vd falls outside thenormal range (step S3, N), that the insulation resistance is abnormal(dielectric breakdown has occurred) (step S4).

On recognizing that the insulation resistance of the power supplycircuit 1 b is abnormal, the controller 15 ends the insulationresistance detection operation. Here, the controller 15 can be soconfigured as to give off a predetermined alarm A (display, sound, orotherwise indicate it) to notify that the insulation resistance of thepower supply circuit 1 b is abnormal. This permits the user to recognizethat dielectric breakdown has occurred and that it has occurred in thepower supply circuit 1 b.

On the other hand, on detecting that the insulation resistance of thepower supply circuit 1 b is normal, the controller 15 turns on the powerswitch Sw3 (step S5). As a result, via the power switch Sw3, theinverter circuit 1 c now conducts to the positive electrode of the DCpower source 1 a, and thus the smoothing capacitor 21 is charged. Atthis stage, the upper-arm switching devices (Sw4, Sw6, Sw8) in theinverter circuit 1 c are all still off, and accordingly the portion onthe succeeding-stage side of those switching devices (that is, the motor2) does not conduct to the positive electrode of the DC power source 1a.

In this state, the controller 15 checks whether or not the voltage valueVd falls within the prescribed normal range (step S6). This operation isaimed at checking whether or not the insulation resistance of theinverter circuit 1 c (the portion on the succeeding-stage side of thepower switch Sw3 and on the preceding-stage side of the upper arms ofthe inverter circuit 1 c) is satisfactory.

When the insulation resistance in the inverter circuit 1 b issufficiently high (normal), the voltage value Vd is close to the valueof the voltage resulting from division of the voltage of the DC powersource 1 a by the resistors (11 to 14). However, the lower theinsulation resistance (that is, the more serious the abnormality), thefarther the voltage value Vd deviates from the value of the voltageresulting from division of the voltage of the DC power source 1 a by theresistors (11 to 14).

Through the insulation resistance detection operation thus far, it isalready found that the insulation resistance of the power supply circuit1 b is normal. Accordingly, if the voltage value Vd is a value deviatedfrom the value of the voltage resulting from division of the voltage ofthe DC power source 1 a by the resistors (11 to 14), it can be concludedthat the cause is a low insulation resistance in the inverter circuit 1b.

Based on this principle, the controller 15 recognizes, when the voltagevalue Vd falls within the normal range (step S6, Y), that the insulationresistance of the inverter circuit 1 c is normal (no dielectricbreakdown has occurred) and, when the voltage value Vd falls outside thenormal range (step S6, N), that the insulation resistance is abnormal(dielectric breakdown has occurred) (step S7).

On recognizing that the insulation resistance of the inverter circuit 1c is abnormal, the controller 15 ends the insulation resistancedetection operation. Here, the controller 15 can be so configured as togive off a predetermined alarm B (different from alarm A) to notify thatthe insulation resistance of the inverter circuit 1 b is abnormal. Thispermits the user to recognize that dielectric breakdown has occurred andthat it has occurred in the inverter circuit 1 c.

On the other hand, on detecting that the insulation resistance of theinverter circuit 1 c is normal, the controller 15 keeps the upper arm ofone phase (for example, the U phase) of the inverter circuit 1 c on fora predetermined period T1 (step S8). Here, so that the upper arm may bekept on properly, first the lower arm of the same phase is kept on for avery short period and, after this lower arm is turned off, the upper armis turned on. With respect to the operation at step S8, the control forturning on the upper and lower arms of the inverter circuit 1 c can bedirectly performed by the controller 15 provided in the power supplycircuit 1 b, or can be performed by an unillustrated microprocessor(capable of operating in coordination with the controller 15 via CAN(controller area network) communication) provided in the invertercircuit 1 c.

As a result, via the upper arm that is now on, the three-phase lines 2 aconduct to the positive electrode of the DC power source 1 a. While theupper arm is on, the controller 15 checks whether or not the voltagevalue Vd falls within the prescribed normal range (step S9). Thisoperation is aimed at checking whether or not the insulation resistanceof the three-phase lines 2 a (the portion on the succeeding-stage sideof the upper arms of the inverter circuit 1 c) is satisfactory.

The above-mentioned period T1 (the period for which the upper arm iskept on) is set to be as short as possible so long as it is possible toproperly check whether or not the insulation resistance of thethree-phase lines 2 a is satisfactory. This makes it possible tominimize the braking torque produced as a result of the upper arms beingturned on while, for example, the user is pushing the electric vehicleby hand.

When the insulation resistance in the three-phase lines 2 a issufficiently high (normal), the voltage value Vd is close to the valueof the voltage resulting from division of the voltage of the DC powersource 1 a by the resistors (11 to 14). However, the lower theinsulation resistance (that is, the more serious the abnormality), thefarther the voltage value Vd is deviated from the value of the voltageresulting from division of the voltage of the DC power source 1 a by theresistors (11 to 14).

Through the insulation resistance detection operation thus far, it isalready found that the insulation resistance is normal with respect tothe power supply circuit 1 b and the inverter circuit 1 c. Thus, whenthe voltage value Vd is deviated from the value of the voltage resultingfrom division of the voltage of the DC power source 1 a by the resistors(11 to 14), it can be concluded that the cause is a low insulationresistance in the three-phase lines 2 a.

Based on this principle, the controller 15 recognizes, when the voltagevalue Vd falls within the normal range (step S9, Y), that the insulationresistance in the three-phase lines 2 a is normal (no dielectricbreakdown has occurred) and, when the voltage value Vd falls outside thenormal range (step S9, N), that the insulation resistance is abnormal(dielectric breakdown has occurred) (step S10). Since the three-phaselines 2 a for the different phases are connected together inside themotor 2, simply by turning on the upper arm of one phase as describedabove, it is possible to detect the insulation resistance for allphases.

On recognizing that the insulation resistance of the three-phase lines 2a is abnormal, the controller 15 ends the insulation resistancedetection operation. Here, the controller 15 can be so configured as togive off a predetermined alarm C (different from alarms A and B) tonotify that the insulation resistance of the three-phase lines 2 a isabnormal. This permits the user to recognize that dielectric breakdownhas occurred and that it has occurred in the three-phase lines 2 a.

On the other hand, if the insulation resistance of the three-phase lines2 a is found to be normal, this means that it has been recognized thatthe insulation resistance is normal with respect to all of the powersupply circuit 1 b, the inverter circuit 1 c, and the three-phase lines2 a. Accordingly, in this case, the controller 15 recognizes that theinsulation resistance is normal in the entire motor device 9 (nodielectric breakdown has occurred) (step S11), and ends the insulationresistance detection operation.

[Features of the Motor Driving Circuit]

As described above, the motor driving circuit 1 according to the firstembodiment is provided with: a supply line L1 connected to a DC powersource 1 a; an inverter circuit 1 c of which the input side is connectedto the supply line L1 and of which the output side is connected to amotor 2, the inverter circuit 1 c converting DC electric power fed fromthe supply line L1 into alternating-current electric power and feedingthe alternating-current electric power to the motor 2; and a powerswitch Sw3 inserted in the supply line L1 (for example, as in thisembodiment, between the DC power source 1 a and the inverter circuit 1c) for switching the supply line L1 between a conducting state and acut-off state.

The motor driving circuit 1 is further provided with: a functionalportion (voltage detector) for detecting the voltage between the DCpower source 1 a and the power switch Sw3; and a functional portion(insulation resistance detector) for first performing a first detectionoperation to detect, based on the result of detection by the voltagedetector with the power switch Sw3 in the cut-off state, the insulationresistance of the power supply circuit 1 b (on the preceding-stage sideof the power switch Sw3), and subsequently performing a second detectionoperation to detect, based on the result of detection by the voltagedetector with the power switch Sw3 in the conducting state, theinsulation resistance of the inverter circuit 1 c (on thesucceeding-stage side of the power switch Sw3).

Thus, the motor driving circuit 1 can detect insulation resistanceseparately for different portions of the motor device 9 (in thisembodiment, for each of the power supply circuit 1 b and the invertercircuit 1 c), and in addition, owing to insulation resistance detectionfor different portions being achieved by a common circuit, allows easysimplification of circuit configuration. “Portion-by-portion” detectionof insulation resistance can be implemented in any other manner than inthis embodiment. In one possible embodiment, insulation resistance canbe detected for each of a portion (DC-side) where DC power is used and aportion (AC-side) where AC power is used. I this embodiment, the firstdetection operation corresponds to the operation at step S3, and thesecond detection operation corresponds to the operation at step S6.

The inverter circuit 1 c has three-phase arms, and each arm includes anupper device and a lower device as switching devices connected in seriesbetween the positive electrode and the negative electrode of the DCpower source 1 a. Between the upper and lower devices of each arm, athree-phase motor 2 is connected. The insulation resistance detectorperforms, as the second detection operation, an operation to detect,based on the result of detection by the voltage detector with all theupper devices in an off state, the insulation resistance of the invertercircuit 1 c (on the preceding-stage side of the upper devices), andperforms, subsequently to the second detection operation, as a thirddetection operation, an operation to detect, based on the result ofdetection by the voltage detector with one of the upper devices in an onstate, the insulation resistance of three-phase lines 2 a of the motor(on the succeeding-stage side of the upper devices).

Thus, the motor driving circuit 1 can detect, with a common circuit, theinsulation resistance of the power supply circuit 1 b, that of theinverter circuit 1 c, and that of the three-phase lines 2 a. In thisembodiment, the third detection operation corresponds to the operationat step S9. Although in this embodiment the inverter circuit 1 c and themotor 2 are of a three-phase type, they can instead be of a single-phasetype, or of a two-phase, four-phase, or any other multiple-phase type.

In the motor driving circuit 1, when an abnormal insulation resistanceis detected in any of the first to third detection operations, an output(alarm A, B, or C) that is set to differ among the different detectionoperations is delivered. Thus, when dielectric breakdown has occurred,the user can identify its location among different portions of the motordevice 9. This permits the user to react more properly than when thelocation is not identified.

In the motor driving circuit 1, when an abnormal insulation resistanceis detected in any of the first to third detection operations, executionof any detection operation thereafter is omitted. Specifically, if anabnormal insulation resistance is detected in the first detectionoperation, execution of the second and third detection operations isomitted; if an abnormal insulation resistance is detected in the seconddetection operation, execution of the third detection operation isomitted. This prevents execution of an unnecessary detection operation,and helps reduce the operation burden on the motor driving circuit 1.

2. Second Embodiment

Next, a second embodiment of the present invention will be described.The following description focuses on features different from the firstembodiment, and overlapping description of common features areoccasionally omitted.

[Configuration and Other Features of a Motor Device]

FIG. 3 is a configuration diagram of a motor device 9A according to thesecond embodiment. In the motor device 9A, two motors (2 _(L), 2 _(R))are connected to a motor driving circuit 1. More specifically, the motordriving circuit 1 has an inverter circuit and other componentsseparately in each of two groups, namely a left group and a right group,so that the motor 2 _(L) belonging to the left group is connected to aleft-group inverter circuit 1 c _(L) and the motor 2 _(R) belonging tothe right group is connected to a right-group inverter circuit 1 c _(R).The subscripts “L” and “R” in reference signs indicate association withthe left and right groups respectively.

The motor device 9A is provided on an electric vehicle that has drivingwheels separately on the left and right sides respectively, theleft-group motor 2 _(L) serving to rotate the driving wheel on the leftside and the right-group motor 2 _(R) serving to rotate the drivingwheel on the right side. The motor device 9A can be incorporated in anyof various electric vehicles, such as three-wheel electric vehicles andfour-wheel electric vehicles, irrespective of the number of wheels. Whenincorporated in a three-wheel electric vehicle having one front wheeland two, i.e. left and right, rear wheels (driving wheels), the motordevice 9A rotates the rear wheels; when incorporated in a three-wheelelectric vehicle having two, i.e. left and right, front wheels (drivingwheels) and one rear wheel, the motor device 9A rotates the frontwheels.

The motor driving circuit 1 has a DC power source 1 a, a power supplycircuit 1 b, a left-group inverter circuit 1 c _(L), and a right-groupinverter circuit 1 c _(R). The power supply circuit 1 b, the invertercircuits (1 c _(L), 1 c _(R)), and the motors (2 _(L), 2 _(R)) arehoused in separate metal cases (5 a, 5 b _(L), 5 b _(R), 5 c _(L), 5 c_(R)) respectively. These metal cases (5 a, 5 b _(L), 5 b _(R), 5 c_(L), 5 c _(R)) are connected together via the body frame of theelectric vehicle.

The DC power source 1 a is similar to the one in the first embodiment.The positive electrode side of the DC power source 1 a is connected to apositive line L1 (supply line), and the negative electrode side of theDC power source 1 a is connected to a negative line L2 (ground line).The DC power source 1 a, the power supply circuit 1 b, and the invertercircuits (1 c _(L), 1 c _(R)) are connected together via the positiveline L1 and the motor 2. The positive line L1 has a single line betweenthe positive electrode of the DC power source 1 a and a branch point P,and is branched, on the succeeding-stage side of the branch point P,into two lines belonging to the left and right groups respectively.

The power supply circuit 1 b has four resistors (11 to 14), a controller15, a left-group power switch Sw3 _(L), a right-group power switch Sw3_(R), and two normally-open switches (Sw1, Sw2).

The power switches (Sw3 _(L), Sw3 _(R)) are each a FET, the channelacross whose both terminals (source and drain) is controlled between anopen and a closed state (an on and an off state) by the controller 15.The left-group power switch Sw3 _(L) is inserted in the left-grouppositive line L1 (on the succeeding-stage side of the branch point P),and serves to switch the left-group positive line L1 between aconducting and a cut-off state. The right-group power switch Sw3 _(R) isinserted in the right-group positive line L1 (on the succeeding-stageside of the branch point P), and serves to switch the right-grouppositive line L1 between a conducting and a cut-off state.

The normally-open switches (Sw1, Sw2) are each a photoMOS relay, thechannel across whose both terminals (source and drain) is controlledbetween an open and a closed state (an on and an off state) by thecontroller 15. One end of the normally-open switch Sw1 is connected viathe resistor 11 to the positive line L1 (on the preceding-stage side ofthe power switches (Sw3 _(L), Sw3 _(R))), and the other end of thenormally-open switch Sw1 is connected to one end of the resistor 12. Theother end of the resistor 12 is connected to one end of the resistor 13.One end of the normally-open switch Sw2 is connected to the other end ofthe resistor 13, and the other end of the normally-open switch Sw2 isconnected via the resistor 14 to the negative line L2.

The connection point between the resistors 12 and 13 is connected to thebody frame of the electric vehicle. The connection point between thenormally-open switch Sw2 and the resistor 14 is connected to thecontroller 15. Thus, when the normally-open switches (Sw1, Sw2) are bothin the closed state, the controller 15 can detect a voltage value Vdwhich results from division of the voltage between the positive line L1and the negative line L2 by the resistors (11 to 14). As in the firstembodiment, a portion of the power supply circuit 1 b serves as aninsulation resistance detection circuit, and the result of the detectionof the voltage value Vd is used in the detection of insulationresistance.

The left-group inverter circuit 1 c _(L) is provided on thesucceeding-stage side of the power supply circuit 1 b. The invertercircuit 1 c _(L) is supplied with a DC voltage from the DC power source1 a, and serves to convert the DC voltage into a three-phase AC(alternating-current) voltage to output it to the left-group motor 2_(L). The inverter circuit 1 c _(L) has a smoothing capacitor 21 _(L)and also three-phase arms comprising a U-phase, a V-phase, and a W-phasearm.

One end of the smoothing capacitor 21 _(L) is connected to theleft-group positive line L1, and the other end of the smoothingcapacitor 21 _(L) is connected to the negative line L2. The U-phase,V-phase, and W-phase arms are connected in parallel, each between theleft-group positive line L1 and the negative line L2.

The U-phase arm has two switching devices (Sw4 _(L) and Sw5 _(L))connected in series between the left-group positive line L1 and thenegative line L2 and two diodes connected in parallel with thoseswitching devices (Sw4 _(L) and Sw5 _(L)) respectively. Each diode isarranged with its cathode pointing to the positive line L1 and its anodepointing to the negative line L2. The switching device Sw4 _(L)corresponds to an upper-arm switch (upper device) of the U phase, andthe switching device Sw5 _(L) corresponds to a lower-arm switch (lowerdevice) of the U phase.

The V-phase arm has two switching devices (Sw6 _(L) and Sw7 _(L))connected in series between the left-group positive line L1 and thenegative line L2 and two diodes connected in parallel with thoseswitching devices (Sw6 _(L) and Sw7 _(L)) respectively. Each diode isarranged with its cathode pointing to the positive line L1 and its anodepointing to the negative line L2. The switching device Sw6 _(L)corresponds to an upper-arm switch (upper device) of the V phase, andthe switching device Sw7 _(L) corresponds to a lower-arm switch (lowerdevice) of the V phase.

The W-phase arm has two switching devices (Sw8 _(L) and Sw9 _(L))connected in series between the left-group positive line L1 and thenegative line L2 and two diodes connected in parallel with thoseswitching devices (Sw8 _(L) and Sw9 _(L)) respectively. Each diode isarranged with its cathode pointing to the positive line L1 and its anodepointing to the negative line L2. The switching device Sw8 _(L)corresponds to an upper-arm switch (upper device) of the W phase, andthe switching device Sw9 _(L) corresponds to a lower-arm switch (lowerdevice) of the W phase.

The switching devices (Sw4 _(L) to Sw9 _(L)) constituting the invertercircuit 1 c _(L) are each a FET, the channel across whose both terminals(source and drain) is controlled between an open and a closed state (anon and an off state) by the controller 15.

The left-group motor 2 _(L) is, for example, a three-phasepermanent-magnet synchronous motor, and is driven by the three-phase ACvoltage fed from the inverter circuit 1 c _(L). The motor 2 _(L) hasthree-phase lines 2 a _(L), which comprise a U-phase, a V-phase, and aW-phase line, and these lines are connected together inside the motor 2_(L). The U-phase, V-phase, and W-phase lines are connected to, insidethe inverter circuit 1 c _(L), between the upper and lower arms of theU, V, and W phases respectively.

The right-group inverter circuit 1 c _(R) is provided on thesucceeding-stage side of the power supply circuit 1 b. The invertercircuit 1 c _(R) is supplied with a DC voltage from the DC power source1 a, and serves to convert the DC voltage into a three-phase AC(alternating-current) voltage to output it to the right-group motor 2_(R). The inverter circuit 1 c _(R) has a smoothing capacitor 21 _(R)and also three-phase arms comprising a U-phase, a V-phase, and a W-phasearm.

One end of the smoothing capacitor 21 _(R) is connected to theright-group positive line L1, and the other end of the smoothingcapacitor 21 _(R) is connected to the negative line L2. The U-phase,V-phase, and W-phase arms are connected in parallel, each between theright-group positive line L1 and the negative line L2.

The U-phase arm has two switching devices (Sw4 _(R) and Sw5 _(R))connected in series between the right-group positive line L1 and thenegative line L2 and two diodes connected in parallel with thoseswitching devices (Sw4 _(R) and Sw5 _(R)) respectively. Each diode isarranged with its cathode pointing to the positive line L1 and its anodepointing to the negative line L2. The switching device Sw4 _(R)corresponds to an upper-arm switch (upper device) of the U phase, andthe switching device Sw5 _(R) corresponds to a lower-arm switch (lowerdevice) of the U phase.

The V-phase arm has two switching devices (Sw6 _(R) and Sw7 _(R))connected in series between the right-group positive line L1 and thenegative line L2 and two diodes connected in parallel with thoseswitching devices (Sw6 _(R) and Sw7 _(R)) respectively. Each diode isarranged with its cathode pointing to the positive line L1 and its anodepointing to the negative line L2. The switching device Sw6 _(R)corresponds to an upper-arm switch (upper device) of the V phase, andthe switching device Sw7 _(R) corresponds to a lower-arm switch (lowerdevice) of the V phase.

The W-phase arm has two switching devices (Sw8 _(R) and Sw9 _(R))connected in series between the right-group positive line L1 and thenegative line L2 and two diodes connected in parallel with thoseswitching devices (Sw8 _(R) and Sw9 _(R)) respectively. Each diode isarranged with its cathode pointing to the positive line L1 and its anodepointing to the negative line L2. The switching device Sw8 _(R)corresponds to an upper-arm switch (upper device) of the W phase, andthe switching device Sw9 _(R) corresponds to a lower-arm switch (lowerdevice) of the W phase.

The switching devices (Sw4 _(R) to Sw9 _(R)) constituting the invertercircuit 1 c _(R) are each a FET, the channel across whose both terminals(source and drain) is controlled between an open and a closed state (anon and an off state) by the controller 15.

The right-group motor 2 _(R) is, for example, a three-phasepermanent-magnet synchronous motor, and is driven by the three-phase ACvoltage fed from the inverter circuit 1 c _(R). The motor 2 _(R) hasthree-phase lines 2 a _(R), which comprise a U-phase, a V-phase, and aW-phase line, and these lines are connected together inside the motor 2_(R). The U-phase, V-phase, and W-phase lines are connected to, insidethe inverter circuit 1 c _(R), between the upper and lower arms of theU, V, and W phases respectively.

The controller 15 provided in the power supply circuit 1 b can outputcontrol signals to control the switches (Sw1, Sw2, Sw3 _(L) to Sw9 _(L),Sw3 _(R) to Sw9 _(R)) individually between the on and off states, andcontrols the operation of the motor driving circuit 1 through aprescribed procedure. One example of the operation performed by themotor driving circuit 1 is insulation resistance detection operation fordetecting whether or not the insulation resistance of the motor device 9is satisfactory or not.

[Insulation Resistance Detection Operation]

In an electric vehicle incorporating the motor device 9A, when anignition key is turned on, the vehicle goes through a predeterminedstart-up mode into a running mode in which it can run. In the start-upmode, the motor driving circuit 1 performs insulation resistancedetection operation. Now, the insulation resistance detection operationperformed by the motor driving circuit 1 will be described withreference to a flow chart in FIG. 4. At the stage before the start ofthe insulation resistance detection operation, the switches (Sw1, Sw2,Sw3 _(L) to Sw9 _(L), Sw3 _(R) to Sw9 _(R)) are all off.

First, the controller 15 executes an insulation resistance sensorstart-up conformation (step S21). The insulation resistance sensorstart-up conformation is operation performed, before closing thenormally-open switches (Sw1, Sw2), to check whether or not the detectedvalue of the voltage Vd is normal (whether or not it falls within atolerated error range with respect to 0 V). If the detected value of thevoltage Vd is abnormal, for example, an alarm indicating the abnormalitycan be given off, and the insulation resistance detection operation canbe aborted.

Next, the controller 15 turns on both normally-open switches (Sw1, Sw2)(step S22). As a result, the positive line L1 is connected via theresistors 11 and 12 to the body frame, and the negative line L2 isconnected via the resistors 13 and 14 to the body frame. At this stage,the power switches (Sw3 _(L), Sw3 _(R)) are still off, and accordinglythe portion on the succeeding-stage side of the power switches (Sw3_(L), Sw3 _(R)), that is, the inverter circuits (1 c _(L), 1 c _(R)) andthe motors (2 _(L), 2 _(R)), does not conduct to the positive electrodeof the DC power source 1 a.

In this state, the controller 15 checks whether or not the voltage valueVd falls within a prescribed normal range (step S23). This operation,based on a principle similar to that for the operation at step S3 in thefirst embodiment, is aimed at checking whether or not the insulationresistance of the power supply circuit 1 b (the portion on thepreceding-stage side of the power switches (Sw3 _(L), Sw3 _(R))) issatisfactory. The normal range is determined with consideration givento, for example, fluctuations in the voltage of the DC power source 1 aso that it is possible to properly detect whether or not the insulationresistance is satisfactory.

The controller 15 recognizes, when the voltage value Vd falls within thenormal range (step S23, Y), that the insulation resistance of the powersupply circuit 1 b is normal (no dielectric breakdown has occurred) and,when the voltage value Vd falls outside the normal range (step S23, N),that the insulation resistance is abnormal (dielectric breakdown hasoccurred) (step S24).

On recognizing that the insulation resistance of the power supplycircuit 1 b is abnormal, the controller 15 ends the insulationresistance detection operation. Here, the controller 15 can be soconfigured as to give off a predetermined alarm A (display, sound, orotherwise indicate it) to notify that the insulation resistance of thepower supply circuit 1 b is abnormal. This permits the user to recognizethat dielectric breakdown has occurred and that it has occurred in thepower supply circuit 1 b.

On the other hand, on detecting that the insulation resistance of thepower supply circuit 1 b is normal, the controller 15 turns on theleft-group power switch Sw3 _(L) (step S25). As a result, via theleft-group power switch Sw3 _(L), the left-group inverter circuit 1 c_(L) now conducts to the positive electrode of the DC power source 1 a,and thus the left-group smoothing capacitor 21 _(L) is charged. At thisstage, the upper-arm switching devices (Sw4 _(L), Sw6 _(L), Sw8 _(L)) inthe left-group inverter circuit 1 c _(L) are all still off, andaccordingly the portion on the succeeding-stage side of those switchingdevices (that is, the left-group motor 2 _(L)) does not conduct to thepositive electrode of the DC power source 1 a.

In this state, the controller 15 checks whether or not the voltage valueVd falls within the prescribed normal range (step S26). This operation,on a principle similar to that for the operation at step S6 in the firstembodiment, is aimed at checking whether or not the insulationresistance of the left-group inverter circuit 1 c _(L) (the portion onthe succeeding-stage side of the left-group power switch Sw3 _(L) and onthe preceding-stage side of the upper arms of the left-group invertercircuit 1 c _(L)) is satisfactory.

The controller 15 recognizes, when the voltage value Vd falls within thenormal range (step S26, Y), that the insulation resistance of theleft-group inverter circuit 1 c _(L) is normal (no dielectric breakdownhas occurred) and, when the voltage value Vd falls outside the normalrange (step S26, N), that the insulation resistance is abnormal(dielectric breakdown has occurred) (step S27).

On recognizing that the insulation resistance of the left-group invertercircuit 1 c _(L) is abnormal, the controller 15 ends the insulationresistance detection operation. Here, the controller 15 can be soconfigured as to give off a predetermined alarm B1 (different from alarmA) to notify that the insulation resistance of the left-group invertercircuit 1 c _(L) is abnormal. This permits the user to recognize thatdielectric breakdown has occurred and that it has occurred in theleft-group inverter circuit 1 c _(L).

On the other hand, on detecting that the insulation resistance of theleft-group inverter circuit 1 c _(L) is normal, the controller 15 turnson the right-group power switch Sw3 _(R) (step S28). As a result, viathe right-group power switch Sw3 _(R), the right-group inverter circuit1 c _(R) now conducts to the positive electrode of the DC power source 1a, and thus the right-group smoothing capacitor 21 _(R) is charged. Atthis stage, the upper-arm switching devices (Sw4 _(R), Sw6 _(R), Sw8_(R)) in the right-group inverter circuit 1 c _(R) are all still off,and accordingly the portion on the succeeding-stage side of thoseswitching devices (that is, the right-group motor 2 _(R)) does notconduct to the positive electrode of the DC power source 1 a.

In this state, the controller 15 checks whether or not the voltage valueVd falls within the prescribed normal range (step S29). This operation,on a principle similar to that for the operation at step S6 in the firstembodiment, is aimed at checking whether or not the insulationresistance of the right-group inverter circuit 1 c _(R) (the portion onthe succeeding-stage side of the right-group power switch Sw3 _(R) andon the preceding-stage side of the upper arms of the right-groupinverter circuit 1 c _(R)) is satisfactory.

The controller 15 recognizes, when the voltage value Vd falls within thenormal range (step S29, Y), that the insulation resistance of theright-group inverter circuit 1 c _(R) is normal (no dielectric breakdownhas occurred) and, when the voltage value Vd falls outside the normalrange (step S29, N), that the insulation resistance is abnormal(dielectric breakdown has occurred) (step S30).

On recognizing that the insulation resistance of the right-groupinverter circuit 1 c _(R) is abnormal, the controller 15 ends theinsulation resistance detection operation. Here, the controller 15 canbe so configured as to give off a predetermined alarm B2 (different fromalarms A and B1) to notify that the insulation resistance of theright-group inverter circuit 1 c _(R) is abnormal. This permits the userto recognize that dielectric breakdown has occurred and that it hasoccurred in the right-group inverter circuit 1 c _(R).

On the other hand, on detecting that the insulation resistance of theright-group inverter circuit 1 c _(R) is normal, the controller 15 keepsthe upper arm of one phase (for example, the U phase) of the left-groupinverter circuit 1 c _(L) on for a predetermined period (step S31).Here, so that the upper arm may be kept on properly, first the lower armof the same phase is kept on for a very short period and, after thislower arm is turned off, the upper arm is turned on. With respect to theoperation at step S31, the control for turning on the upper and lowerarms of the inverter circuit 1 c _(L) can be directly performed by thecontroller 15 provided in the power supply circuit 1 b, or can beperformed by an unillustrated microprocessor (capable of operating incoordination with the controller 15 via CAN communication) provided inthe inverter circuit 1 c _(L).

As a result, via the upper arm that is now on, the left-groupthree-phase lines 2 a _(L) conduct to the positive electrode of the DCpower source 1 a. While the upper arm is on, the controller 15 checkswhether or not the voltage value Vd falls within the prescribed normalrange (step S32). This operation, based on a principle similar to thatfor the operation at step S9 in the first embodiment, is aimed atchecking whether or not the insulation resistance of the left-groupthree-phase lines 2 a _(L) (the portion on the succeeding-stage side ofthe upper arms of the left-group inverter circuit 1 c _(L)) issatisfactory.

The controller 15 recognizes, when the voltage value Vd falls within thenormal range (step S32, Y), that the insulation resistance in theleft-group three-phase lines 2 a _(L) is normal (no dielectric breakdownhas occurred) and, when the voltage value Vd falls outside the normalrange (step S32, N), that the insulation resistance is abnormal(dielectric breakdown has occurred) (step S33).

On recognizing that the insulation resistance of the left-groupthree-phase lines 2 a _(L) is abnormal, the controller 15 ends theinsulation resistance detection operation. Here, the controller 15 canbe so configured as to give off a predetermined alarm C1 (different fromalarms A, B1, and B2) to notify that the insulation resistance of theleft-group three-phase lines 2 a _(L) is abnormal. This permits the userto recognize that dielectric breakdown has occurred and that it hasoccurred in the left-group three-phase lines 2 a _(L).

On the other hand, if the insulation resistance of the left-groupthree-phase lines 2 a _(L) is found to be normal, the controller 15keeps the upper arm of one phase (for example, the U phase) of theright-group inverter circuit 1 c _(R) on for a predetermined period(step S34). Here, so that the upper arm may be kept on properly, firstthe lower arm of the same phase is kept on for a very short period and,after this lower arm is turned off, the upper arm is turned on. Withrespect to the operation at step S34, the control for turning on theupper and lower arms of the inverter circuit 1 c _(R) can be directlyperformed by the controller 15 provided in the power supply circuit 1 b,or can be performed by an unillustrated microprocessor (capable ofoperating in coordination with the controller 15 via CAN communication)provided in the inverter circuit 1 c _(R).

As a result, via the upper arm that is now on, the right-groupthree-phase lines 2 a _(R) conduct to the positive electrode of the DCpower source 1 a. While the upper arm is on, the controller 15 checkswhether or not the voltage value Vd falls within the prescribed normalrange (step S35). This operation, based on a principle similar to thatfor the operation at step S9 in the first embodiment, is aimed atchecking whether or not the insulation resistance of the right-groupthree-phase lines 2 a _(R) (the portion on the succeeding-stage side ofthe upper arms of the right-group inverter circuit 1 c _(R)) issatisfactory.

The controller 15 recognizes, when the voltage value Vd falls within thenormal range (step S35, Y), that the insulation resistance in theright-group three-phase lines 2 a _(R) is normal (no dielectricbreakdown has occurred) and, when the voltage value Vd falls outside thenormal range (step S35, N), that the insulation resistance is abnormal(dielectric breakdown has occurred) (step S36).

On recognizing that the insulation resistance of the right-groupthree-phase lines 2 a _(R) is abnormal, the controller 15 ends theinsulation resistance detection operation. Here, the controller 15 canbe so configured as to give off a predetermined alarm C2 (different fromalarms A, B1, B2, and C1) to notify that the insulation resistance ofthe right-group three-phase lines 2 a _(R) is abnormal. This permits theuser to recognize that dielectric breakdown has occurred and that it hasoccurred in the right-group three-phase lines 2 a _(R).

On the other hand, if the insulation resistance of the right-groupthree-phase lines 2 a _(R) is found to be normal, this means that it hasbeen recognized that the insulation resistance is normal with respect toall of the power supply circuit 1 b, the inverter circuits (1 c _(L), 1c _(R)), and the three-phase lines (2 ₄ and 2 a _(R)). Accordingly, inthis case, the controller 15 recognizes that the insulation resistanceis normal in the entire motor device 9A (no dielectric breakdown hasoccurred) (step S37), and ends the insulation resistance detectionoperation.

[Features of the Motor Driving Circuit]

As described above, the motor driving circuit 1 according to the secondembodiment is provided with: a supply line L1 connected to a DC powersource 1 a; an inverter circuit of which the input side is connected tothe supply line L1 and of which the output side is connected to a motor,the inverter circuit converting DC electric power fed from the supplyline L1 into alternating-current electric power and feeding thealternating-current electric power to the motor; and a power switchinserted in the supply line L1 for switching the supply line L1 betweena conducting state and a cut-off state. As the inverter circuit,inverter circuits (1 c _(L), 1 c _(R)) are provided to belong to two,i.e. left and right, groups respectively, and as the power switch, powerswitches (Sw3 _(L), Sw3 _(R)) are provided to belong to two, i.e. leftand right, groups respectively. In this embodiment, as an example,between the DC power source 1 a and the left-group inverter circuit 1 c_(L), the left-group power switch Sw3 _(L) is provided, and between theDC power source 1 a and the right-group inverter circuit 1 c _(R), theright-group power switch Sw3 _(R) is provided.

The motor driving circuit 1 is further provided with: a functionalportion (voltage detector) for detecting the voltage at the locationthat lies between the DC power source 1 a and the left-group powerswitch Sw3 _(L) and simultaneously between the DC power source 1 a andthe right-group power switch Sw3 _(R), that is, the location that lies,with respect to both power switches (Sw3 _(L), Sw3 _(R)), between the DCpower source 1 a and them. The motor driving circuit 1 is furtherprovided with a functional portion (insulation resistance detector) forfirst performing a first detection operation to detect, based on theresult of detection by the voltage detector with the power switches (Sw3_(L), Sw3 _(R)) in the cut-off state, the insulation resistance of thepower supply circuit 1 b (on the preceding-stage side of the powerswitches (Sw3 _(L), Sw3 _(R))), and subsequently performing a seconddetection operation to detect, based on the result of detection by thevoltage detector with the power switches in the conducting state, theinsulation resistance of the inverter circuit (on the succeeding-stageside of the power switches (Sw3 _(L), Sw3 _(R))). The second detectionoperation is performed separately for each of the left and right groups.

Thus, the motor driving circuit 1 can detect insulation resistanceseparately for different portions of the motor device 9 (in thisembodiment, for each of the power supply circuit 1 b and the invertercircuits (1 c _(L), 1 c _(R))), and in addition, owing to insulationresistance detection for different portions being achieved by a commoncircuit, allows easy simplification of circuit configuration. In thisembodiment, the first detection operation corresponds to the operationat step S23, and the second detection operation corresponds to theoperation at steps S26 and S29.

Each of the inverter circuits (1 c _(L), 1 c _(R)) has three-phase arms,and each arm includes an upper device and a lower device as switchingdevices connected in series between the positive electrode and thenegative electrode of the DC power source 1 a. Between the upper andlower devices of each arm, three-phase motors (2 _(L), 2 _(R)) areconnected. The insulation resistance detector performs, as the seconddetection operation, an operation to detect, based on the result ofdetection by the voltage detector with all the upper devices in an offstate, the insulation resistance of the inverter circuit (on thepreceding-stage side of the upper devices), and performs, subsequentlyto the second detection operation, as a third detection operation, anoperation to detect, based on the result of detection by the voltagedetector with one of the upper devices in an on state, the insulationresistance of three-phase lines of the motor (on the succeeding-stageside of the upper devices). The third detection operation is performedseparately for each of the left and right groups.

Thus, the motor driving circuit 1 can detect, with a common circuit, theinsulation resistance of the power supply circuit 1 b, those of theinverter circuits (1 c _(L), 1 c _(R)) respectively, and those of thethree-phase lines (2 a _(L), 2 a _(R)) respectively. In this embodiment,the third detection operation corresponds to the operation at steps S32and S35. Although in this embodiment the inverter circuit 1 c and themotor 2 are of a three-phase type, they can instead be of a single-phasetype, or of a two-phase, four-phase, or any other multiple-phase type.

The motor driving circuit 1 can be understood to be provided withinverter circuits (1 c _(L), 1 c _(R)) provided in parallel to belong toa left and a right group respectively, and a plurality of power switches(Sw3 _(L), Sw3 _(R)) provided to belong to the left and right groupsrespectively. It can then be understood that the voltage detector servesto detect the voltage between the DC power source 1 a and each powerswitch, and that the insulation resistance detector first performs, asthe first detection operation, an operation to detect, based on theresult of detection by the voltage detector with all the power switchesin a cut-off state, the insulation resistance on the preceding-stageside of the power switches and subsequently performs the second andthird detection operations for each of the left and right groups.

More specifically, the insulation resistance detector is configured toperform the second detection operation for each of the left and rightgroups and then perform the third detection operation for each of theleft and right groups. In this way, the motor driving circuit 1 candetect, one after the next, the insulation resistance of the powersupply circuit 1 b, those of the inverter circuits (1 c _(L), 1 c _(R))respectively, and those of the three-phase lines (2 a _(L), 2 a _(R))respectively.

In the motor driving circuit 1, when an abnormal insulation resistanceis detected in any of the first to third detection operations, an output(alarm A, B1, B2, C1, or C2) that is set to differ among the differentdetection operations is delivered. Thus, when dielectric breakdown hasoccurred, the user can identify its location among different portions ofthe motor device 9A. This permits the user to react more properly thanwhen the location is not identified.

In the motor driving circuit 1, when an abnormal insulation resistanceis detected in any of the first to third detection operations, executionof any detection operation thereafter is omitted. Specifically, if anabnormal insulation resistance is detected in the first detectionoperation, execution of the second and third detection operations isomitted; if an abnormal insulation resistance is detected in the seconddetection operation, execution of the third detection operation isomitted. This prevents execution of an unnecessary detection operation,and helps reduce the operation burden on the motor driving circuit 1.

The motor device 9 according to the second embodiment is so implementedas to have an inverter circuit 1 b, a motor 2, and other componentsseparately for each of two, i.e., left and right, groups. In a modifiedexample, the motor device 9 can have three or more such groups. Also inthat case, the motor device 9 can perform insulation resistancedetection operation to detect insulation resistance separately fordifferent portions in a manner confirming to this embodiment.

3. Other

The present invention can be implemented in any other manner thanspecifically described by way of embodiments above, with manymodifications made within the spirit of the invention. That is, theembodiments presented above should be understood to be in every aspectillustrative and not restrictive. The technical scope of the presentinvention is defined not by the description of embodiments given above,but by the appended claims, and should be understood to encompass anymodifications made in the sense and scope equivalent to those of theappended claims.

For example, although in both embodiments, the motor driving circuit 1is applied to an electric vehicle and serves to rotate a driving wheel,this is not meant to limit the scope of application of the presentinvention in any way. Motor driving circuits according to the presentinvention find various applications involving motors.

INDUSTRIAL APPLICABILITY

The present invention finds applications, for example, in electricvehicles.

LIST OF REFERENCE SIGNS

-   -   1 motor driving circuit    -   1 a DC power source    -   1 b power supply circuit    -   1 c, 1 c _(L), 1 c _(R), inverter circuit    -   2, 2 _(L), 2 _(R) motor    -   2 a, 2 a _(L), 2 a _(R) three-phase lines    -   5 a-5 c, 5 b _(L), 5 c _(L), 5 b _(R), 5 c _(R) metal case    -   9, 9A motor device    -   11-14 resistor    -   15 controller    -   21, 21 _(L), 21 _(R) smoothing capacitor    -   L1 positive line (supply line)    -   L2 negative line    -   Sw1, Sw2 normally-open switch    -   Sw3, Sw3 _(L), Sw3 _(R) power switch    -   Sw4, Sw4 _(L), Sw4 _(R) switching device (U-phase upper device)    -   Sw5, Sw5 _(L), Sw5 _(R) switching device (U-phase lower device)    -   Sw6, Sw6 _(L), Sw6 _(R) switching device (V-phase upper device)    -   Sw7, Sw7 _(L), Sw7 _(R) switching device (V-phase lower device)    -   Sw8, Sw8 _(L), Sw8 _(R) switching device (W-phase upper device)    -   Sw9, Sw9 _(L), Sw9 _(R) switching device (W-phase lower device)

1. A motor driving circuit, comprising: a supply line connected to a direct-current power source; an inverter of which an input side is connected to the supply line and of which an output side is connected to a motor, the inverter converting direct-current electric power fed from the supply line into alternating-current electric power and feeding the alternating-current electric power to the motor; a power switch inserted in the supply line for switching the supply line between a conducting state and a cut-off state; a voltage detector for detecting a voltage between the direct-current power source and the power switch; and an insulation resistance detector for first performing a first detection operation to detect, based on a result of detection by the voltage detector with the power switch in the cut-off state, an insulation resistance on a preceding-stage side of the power switch and subsequently performing a second detection operation to detect, based on a result of detection by the voltage detector with the power switch in the conducting state, an insulation resistance on a succeeding-stage side of the power switch.
 2. The motor driving circuit according to claim 1, wherein the power switch is provided between the direct-current power source and the inverter.
 3. The motor driving circuit according to claim 2, wherein the inverter has an arm for a single phase, or arms for a plurality of phases, the arm, or each of the arms, includes an upper device and a lower device as switching devices connected in series between a positive electrode and a negative electrode of the direct-current power source, the motor is connected between the upper and lower devices, and the insulation resistance detector performs, as the second detection operation, an operation to detect, based on a result of detection by the voltage detector with every upper device in an off state, an insulation resistance on a preceding-stage side of the upper device, and performs, subsequently to the second detection operation, as a third detection operation, an operation to detect, based on a result of detection by the voltage detector with at least one upper device in an on state, an insulation resistance on a succeeding-stage side of the upper device.
 4. The motor driving circuit according to claim 3, wherein the inverter has, as the arms, three-phase arms, and has, as the motor, a three-phase motor connected between the upper and lower devices of each of the arms, and the insulation resistance detector performs, as the second detection operation, an operation to detect, based on a result of detection by the voltage detector with every upper device in an off state, an insulation resistance of the inverter, and performs, as the third detection operation, an operation to detect, based on a result of detection by the voltage detector with at least one upper device in an on state, an insulation resistance of three-phase lines of the motor.
 5. The motor driving circuit according to claim 3, wherein the inverter comprises inverters provided in parallel to belong to a plurality of groups respectively, the power switch comprises a plurality of power switches provided to belong to the plurality of groups respectively, the voltage detector detects, for each of the power switches, the voltage between the direct-current power source and the power switch, and the insulation resistance detector first performs, as the first detection operation, an operation to detect, based on a result of detection by the voltage detector with all the power switches in a cut-off state, an insulation resistance on a preceding-stage side of all the power switches, and subsequently performs the second and third detection operations for each of the plurality of groups.
 6. The motor driving circuit according to claim 5, wherein the insulation resistance detector performs the second detection operation for each of the plurality of groups, and subsequently performs the third detection operation for each of the plurality of groups.
 7. The motor driving circuit according to claim 3, wherein, when an abnormal insulation resistance is detected in any of the first to third detection operations, an output that is set to differ among the first to third detection operations is delivered.
 8. The motor driving circuit according to claim 3, wherein, when an abnormal insulation resistance is detected in any of the first to third detection operations, execution of any detection operation thereafter is omitted.
 9. A motor device, comprising: a motor driving circuit according to claim 1; and a motor connected to the output side of the inverter.
 10. An electric vehicle, comprising: the motor device according to claim 9; and a driving wheel rotated by the motor.
 11. An electric vehicle, comprising: a motor driving circuit according to claim 1, wherein the inverter comprises inverters provided to belong to two groups respectively, a left driving wheel and a right driving wheel; a left motor connected to an output side of one of the inverters, for rotating the left driving wheel; a right motor connected to an output side of the other of the inverters, for rotating the right driving wheel. 